1. Field of the Invention
This invention relates generally to the field of vehicle navigation systems, and, more particularly, to vehicle navigation systems which can be utilized when lane line markings have become degraded, obscured, or are nonexistent.
2. Related Art
Active safety and driver assist features such as lane departure warning, low-speed lane keeping (Traffic Jam Assist—TJA), high speed lane keeping (Highway Assist—HA) as well as fully autonomous vehicle operation rely upon localization of the vehicle within the lane to provide their functionality. Localization is defined as a computational problem of constructing or updating a map of an unknown environment while simultaneously keeping track of a vehicle's location within it. In general, each of these systems relies upon multiple sensor suites to provide robust and accurate positioning. Examples of currently relied upon sensor suites are: camera, stereo cameras, Global Positioning System (GPS), and LIDAR. However, in instances when lane lines become degraded, obscured, or are nonexistent, the camera and LIDAR based solutions are prone to failure. In addition, GPS on its own is not accurate enough for lane-level localization and is prone to dropping out as a result of urban or natural canyon scenarios.
To facilitate the continued use of these active safety/driver assist features during occasions when positioning sensors operate in a high error or even failed state it is possible to dead reckon based on the last known position, as well as knowledge of the trajectory of the vehicle. It is possible to perform this reckoning using the vehicle on-board Inertial Measurement Unit (IMU) sensors, which are a suite of body fixed accelerometers and gyroscopes used to estimate vehicle velocity states. However, when integrating these signals in an effort to estimate position states, small bias errors can quickly accumulate into large position estimation errors.
An improved reckoning of position state can be achieved via odometry from the vehicle's four wheel-speed sensors. While these sensors provide a robust estimate of longitudinal position, they are unable to accurately estimate lateral position changes of the vehicle. Thus, in the event of faulty or nonexistent lane level perception data, limited, if any, solutions exist for continued operation of the aforementioned active safety and vehicle assist features.